Slip clutch drive mechanism

ABSTRACT

A substantially constant torque is transmitted to a braked shaft through a slip clutch including a wheel-like drive member supported for rotation by the shaft and having angularly disposed axial holes which receive corresponding balls. Compression springs are positioned within the holes to urge the balls into engagement with an annular driven member which is secured to the shaft and has angularly disposed V-shaped peripheral recesses for receiving the balls. The recesses and balls are angularly spaced and arranged so that at least one ball is seated in drive position (within a recess) at substantially any angular position of the drive member relative to the driven member to assure immediate rotative movement of the shaft when the brake is released. An axially adjustable plate rotates with the drive member and engages the springs to provide for conveniently changing the substantially constant torque transmitted to the shaft through the balls and the driven member. The clutch functions in the same manner in either direction of rotation of the drive member.

[451 Aug. 28,1973

l Umted States Patent 1 Briggs SLIP CLUTCH DRIVE MECHANISM [75]inventor: Forrest A. Briggs, DaytomOhio [73] Assignee: The StandardRegister Company,

Dayton, Ohio [22] Filed: Sept. 13, 1971 [211 App]. No.: 179,942

[52] US. Cl. 64/29, 192/12 D, 192/56 R, 192/27 [51] Int. Cl. Fl6d 7/06[58] Field of Search 64/28 R, 29; 192/27, 192/56 R, 67 R, 46, 2, 12 D[56] References Cited UNITED STATES PATENTS 2,351,997 6/1944 Morrill .Q192/12 D 2,539,836 1/1951 Hoffmann. 192/12 D 3,344,292 9/1967 Hurst192/12 D 3,367,460 2/1968 Wanner 192/12 B 3,608,686 9/1971 Martin et a1.64/29 865,486 9/1907 Gannon 64/29 651,706 6/1900 Forbes 192/46 728,8025/1903 Kuhlewind 192/46 1,021,386 3/1912 Uhlig 192/67 R 1,104,211 7/1914Meredith-Jones 64/29 3,599,781 8/1971 Hoadley 64/29 PrimaryExaminer-Manuel A. Antonakas Assistant Examiner-Randall I-lealdAttomey-William' R. Jacox et al.

[ 5 7] ABSTRACT A substantially constant torque is transmitted to abraked shaft through a slip clutch including a wheellike drive membersupported for rotation by the shaft and having angularly disposed axialholes which receive corresponding balls. Compression springs arepositioned within the holes to urge the balls into engagement with anannular driven member which is secured to the shaft and has angularlydisposed V-shaped peripheral recesses for receiving the balls. Therecesses and balls are angularly spaced and arranged so that at leastone ball is seated in drive position (within a recess) at substantiallyany angular position of the drive member relative to the driven memberto assure immediate rotative movement of the shaft when the brake isreleased. An axially adjustable plate rotates with the drive member andengages the springs to provide for conveniently changing thesubstantially constant torque transmitted to the shaft through the ballsand the driven member. The clutch functions in the same manner in eitherdirection of rotation of the drive member.

7 Claims, 6 Drawing Figures Patented Aug. 28, 1973 3,754,412

M/VENTUR FORREST A. BRIGGS A TTOR/VE Y8 SLIP CLUTCH DRIVE MECHANISMBACKGROUND OF THE INVENTION In a drive system as disclosed in U. S. Pat.No. 3,390,629 which issued to the assignee of the present invention andwhich is used for advancing a data card support carriage in astep-by-step manner, it is desirable to employ a brake and a slip clutchfor indexing a shaft which supports a pinion in engagement with a rackextending along the carriage. The shaft is positively braked againstrotation by a solenoid actuated pawl which, engages a toothed brakewheel secured to the shaft. When the solenoid is momentarily energizedto release the brake by retracting the pawl, the carriage is advancedone step by the torque transmitted to the shaft through the slip clutch.

To obtain high speed step-by-step advancement of the data card supportcarriage, it is desirable for a substantially constant torque to becontinuously transmitted to the carriage drive shaft so that the shaftand carriage immediately advance when the solenoid actuated brake ismomentarily released. One form of torque slip clutch which has beenproposed employs a pad of rigid clutch material which is compressedbetween the opposing faces of the drive and driven members. However, ithas been found'that this type of clutch generates substantial heat whenit is subjected to substantial slippage, and the heat affects thecharacteristics of the clutch material, causing a change in the torquewhich is being transmitted=by the clutch. That is, the substantialslippage causes a residue to be released from the faces of the clutchpad thereby causing glazing of the faces and a. corresponding change inthe coefficient of friction of the pad.

There are a number of U. S. patents disclosing slip clutches whichincorporate a plurality of spring loaded balls in one member and acorresponding plurality of semi-spherical cavities or recesses withinthe other member. For example. U. S. Pat. No. 651,706 and No. 1,496,577disclose slip clutches wherein a plurality of balls are spring loaded ina radial direction, and U. S. Pat. No. 865,486 and No. 2,806,366disclose slip clutches having a plurality of balls which are springloaded in an axial direction. The slip clutch disclosed in each of thesepatents presents the problem that the torque transmission is notsubstantially constant,. but fluctuates significantly as the balls rollsimultaneously in and out of the recesses when slippage occurs. Thisfluctuation of torque is particularly undesirable in a drive system foradvancing a data card support carriage as shown in above US. Pat. No.3,390,629 since the torque fluctuation does not provide for immediatemovement of the carriage when the driven member is released and thusdoes not provide for step-by-step advancement of the carriage in arapid, smooth'and uniform manner. I

SUMMARY OF THE INVENTION The present invention is directed to animproved bidirectional slip clutch which is ideally suited for use in adrive for producings step-by-step advancement of a data card supportcarriage, but may also be used in other drives whenever the transmissionof substantially constant torque is desired. The slip clutch of theinvention is especially desirable when substantial slippage is requiredin the drive system and also provides the important advantages of a longand dependable service life with the minimum of maintanence.

The slip clutch of the invention is positioned between a constantlyrotating drive member and a driven member which is held against rotationuntil rotation of thedriven member is desired. As a result of thetransmission of substantially constant torque by the slip clutch, thedriven member rotates substantially immediately when the drivenmember'is released. In accordance with one embodiment of the invention,the drive member is mounted on a shaft for relative rotation and isdriven by a suitable drive. A plurality of angularly spaced holes extendaxially within the drive member and receive corresponding balls whichare urged by corresponding compression springs towards a plate securedto the shaft and having peripherally spaced V- shaped recesses forreceiving the balls. The springs extend from a common annular adjustmentplate which rotates with the drive member, and the balls and recessesare angularly spaced and arranged so that there is always at least oneball seated in driving relation within one of the recesses at anyparticular position of the drive member relative to the driven member.As a result, when the shaft is momentarily released by actuation of abrake, the shaft is immediately rotated or advanced due to thesubstantially constant torque being transmitted from the drive member tothe driven member through the rolling balls.

Other features and advantages of the invention will be apparent from thefollowing description, the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of adrive mechanism incorporating a slip clutch constructed and assembled inaccordance with the invention; 7

FIG. 2 is a fragmentary axial section of the slip clutch in FIG. 1 andshowing one position of a spring biased driving ball;

FIG. 3 is a full axial section of the slip clutch in FIG. 1 and showingone of the balls in its driving position;

FIG. 4 is a perspective exploded view of the slip clutch assembly shownin FIG. 3;

FIG. 5 is an enlarged fragmentary section taken generally on the line 55of FIG. 4 and illustrating the rolling path of a driving ball; and

FIG. 6 is a diagrammatic linear development of the angular arrangementand spacing of the driving balls and recesses employed in the slipclutch shown in FIGS. 1-4.

DESCRIPTION OF TI-IEPREFERRED EMBODIMENT As mentioned above, the drivesystem shown in FIG. I is particularly suited for producing precisestep-bystepvadvancement of a-data card support carriage as disclosed inthe above US. Pat. No. 3,390,629. Preferably, the drive system includesan elongated shaft 20 having each end supported by an anti-frictionbearing block assembly 21. A gear 23 is rigidly secured to the shaft 20and engages an elongated rack 24 which is adapted to be secured to thedata card support carriage in a suitable manner, for example, asillustrated in the above us. Pat. No. 3,390,629.

In accordance with the present invention, an annular drive member orwheel 25 is mounted for rotation on the shaft 20 and includes asleeve-type bronze bearing 27 which receives the shaft 20. The drivewheel 25 has peripherally spaced teeth 28 which are engaged by anendless gear belt 30 extending around the wheel 25 and also around adrive pinion 31 mounted on a shaft 32 connected to a suitable drivemotor 35. A series of six axially extending holes 38 are formed withinthe drive wheel 25, and the holes are arranged in three pairs, with eachpair of holes located approximately 120 from the other two pairs ofholes. The angular spacing between the holes of each pair isapproximately 45.

A brake wheel 40 is rigidly secured to the shaft by a cross pin 41 andincludes peripherally spaced teeth 42 which are adapted to beselectively engaged by a stop pawl 43 actuated by a solenoid 45. In amanner as disclosed in above US. Pat. No. 3,390,629, the pawl 43 isspring biased towards the brake wheel 40 and prevents rotation of thebrake wheel and shaft 20 until the solenoid 45 is energized to retractthe pawl 43.

Referring to FIG. 3, an annular clutch plate 48 is positionedconcentrically with the shaft 20 and is rigidly secured to the brakewheel 40 by a series of axially extending screws 49. As shown in FIGS. 4and 5, the outer peripheral portion of the clutch plate 48 is deformedin a zig-zag manner to define peripherally spaced recesses or grooves 52each of which is defined by a set of flat surfaces 53 disposed to forman included angle of approximately 120. As illustrated diagrammaticallyin FIG. 6, the peripheral portion of the clutch plate 48 has sixteenuniformly spaced recesses or grooves 52 which are located at a diameterto be in opposing relation to the holes 38 within the drive wheel 25.

A ball 55 is located within each of the holes 38 within the drive wheel25, and each ball 55 is urged into engagement with the clutch plate 48by a seat member 58, preferably formed of a low friction plasticsmaterial, and a compression spring 59 which extends between the seatmember 58 and an annular concentric spring retaining plate 60. Locatingstuds 62 project from the plate 60 into the adjacent end portions of thesprings 59, and a pair of diametrically spaced pins 64 project axiallyfrom the plate 60 into corresponding bores or holes 66 formed within thedrive wheel between the ball retaining holes 38 so that the plate 60rotates with the drive wheel 25. 7

An antifriction thrust bearing 70 is mounted on the shaft 20 between thedrive wheel 25 and an externally threaded sleeve 72 which is rigidlysecured to the shaft 20 by a cross pin 73. A washerlike bronze bearing74 surrounds the sleeve 72 and is positioned between the springretaining plate 60 and a pairof lock nuts 76 threaded on the sleeve 72.Thus the force at which the balls 55 are urged axially against theclutch plate 48 may be conveniently adjusted simply by adjusting theaxial position of the lock nuts 76 on the threaded sleeve 72.

When the drive mechanism shown in FIG. I is used for producing rapidstep-by-step advancement of a data card support carriage as shown inabove US. Pat. No. 3,360,629, the drive wheel 25 is rotated continuouslyat a predetermined speed through the gear belt 30. While the card isbeing punched, the shaft 20 is prevented from rotating by engagement ofthe stop pawl 43 with the brake wheel 40. Thus during this short timeperiod, the drive wheel 25 is rotating relative to the clutch plate 48causing the balls 55 to roll in and out of the recesses or grooves 52 asillustrated in FIG. 5.

As a result of the particular angular spacing of the holes 38 and ballsrelative to the uniform angular spacing of the grooves 52, there isalways one ball 55 which is substantially seated within a groove 52regardless of the position of the drive wheel 25 relative to the clutchplate 48. For example, the ball 55 shown at the left end of FIG. 6 isseated in driving relation within one of the grooves 52, and afterslight additional relative rotation between the drive wheel 25 and theclutch plate 48, the adjacent ball 55 shown at the right end of FIG. 6will be located or seated in driving relation within the adjacent groove52. Thus when the brake wheel 40 is mementarily released by retractionof the pawl 43, the brake wheel 40 and the shaft 20 rotate immediatelywith the drive wheel 25 due to the substantially constant torque beingtransmitted by the balls 55 to the clutch plate 48.

It is apparent that the substantially constant torque being transmittedmay be increased or decreased by different means. For example, thesprings 59 may be removed and replaced by springs constructed of wirehaving a different diameter, or the clutch plate 48 may be replaced byanother clutch plate having grooves formed by surfaces 53 defining adifferent included angle therebetween. It is also apparent that thelevel of substantially constant torque being transmitted from the drivewheel 25 to the clutch plate 48 may be conveniently changed by adjustingthe axial position of the lock nuts 76 on the threaded sleeve 72,thereby adjusting the axial position of the spring retaining plate andthe force exerted by the balls 55 against the clutch plate 48.

From the drawing and the above description, it is apparent that a slipclutch constructed in accordance with the present invention, providesdesirable features and advantages. For example, as a result of therolling contact between the balls 55 and the clutch plate 48, the slipclutch is ideally suited for drive systems where substantial slippage isrequired. The slip clutch is bidirectional and is effective to transmita substantially constant torque which can be conveniently changed asdesired and thus is particularly useful in a drive mechanism providingfor positive, rapid and dependable intermittent or step-by-step motionin precise increments and without any significant time delay during eachstep of advancement.

While the form of slip clutch herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of clutch, and that changes may bemade therein without departing from the scope and spirit of theinvention. Furthermore, while the slip clutch is illustrated anddescribed in connection with a drive mechanism for producing precise andrapid step-bystep advancement of a data card support carriage, the slipclutch may be used for many other applications whenever it is desirableto maintain a substantially constant torque between a driven member anda relative rotating driving memberv The invention having been described,the following is claimed:

1. An improved slip clutch comprising a shaft, an annular drive membermounted on said shaft for relative rotation, means for rotating saiddrive member, means defining a plurality of angularly spaced andgenerally axially extending openings within said drive member, a ballwithin each of said openings, an annular brake member positioned on oneside of said drive member and secured to said shaft for rotationtherewith, means forming a plurality of angularly spaced recesses onsaid brake member in axially opposing relation to said balls within saiddrivemember, means for braking the rotation of said brake member andsaid shaft causing said balls to roll between said drive member and saidbrake member, said recesses being arranged relative to said openings toposition at least one of said balls in seating relation within one ofsaid recesses at substantially any angular position of said drive memberrelative to said brake member to provide immediate positive torquetransmission from said drive member to said shaft upon release of saidbraking means, means positioned on the other side of said drive memberfor urging said balls into said recesses, and means for simultaneouslyadjusting the force exerted by said means for urging said balls toprovide for conveniently and precisely adjusting the torque transmissionfrom said drive member to said shaft.

-2. A slip clutch as defined in claim 1 wherein said drive membercomprises a wheel having peripherally spaced teeth and, said rotatingmeans comprise a gear belt.

3. A slip clutch as defined in claim 1 wherein said means forming saidrecesses, comprise a clutch plate positioned between said drive memberand said brake member and having a generally uniform thickness, andmeans for securing said disc to said brake member.

4. A slip clutch as defined in claim 1 wherein said means for urgingsaid balls into said recesses, comprise a plurality of compressionsprings extending within said openings within said'drive member, anannular retaining member surrounding said shaft and confining saidsprings within said openings, and means connecting said retaining memberto said drive member for rotation therewith.

5. A slip clutch as defined in claim 4 wherein said adjustment meanscomprise a tubular threaded bushing secured to said shaft for rotationtherewith, and nut means adjustably mounted on said bushing forconfining said retaining member.

6. An improved slip clutch comprising a shaft, an annular drive membermounted on said shaft for relative rotation, means for rotating saiddrive member, means defining a plurality of angularly spaced andgenerally axially extending openings within said drive member, a ballwithin each of said openings, an annular brake member secured to saidshaft for rotation therewith, a clutch plate positioned axially betweensaid drive memher and said brake member and secured to said brakemember, said clutch plate having a generally uniform thickness and aplurality of angularly spaced grooves in axially opposing relation tosaid balls within said drive member, means for braking the rotation ofsaid brake member and said shaft causing said balls to roll between saiddrive member and said brake member, said grooves being arranged relativeto said openings to position at least one of said balls in seatingrelation within one of said grooves at substantially any angularposition of saiddrive member relative to said brake member to provideimmediate positive torque transmission from said drive member to saidshaft upon release of said braking means, and means for adjusting theforce exerted by said balls against said clutch plate to provide foradjusting the torque transmission from said drive member to said shaft.

7. A slip clutch as defined in claim 6 wherein each said groove isdefined by converging surfaces defining an angle of approximately 120therebetween.

1. An improved slip clutch comprising a shaft, an annular drive membermounted on said shaft for relative rotation, means for rotating saiddrive member, means defining a plurality of angularly spaced andgenerally axially extending openings within said drive member, a ballwithin each of said openings, an annular brake member positioned on oneside of said drive member and secured to said shaft for rotationtherewith, means forming a plurality of angularly spaced recesses onsaid brake member in axially opposing relation to said balls within saiddrive member, means for braking the rotation of said brake member andsaid shaft causing said balls to roll between said drive member and saidbrake member, said recesses being arranged relative to said openings toposition at least one of said balls in seating relation within one ofsaid recesses at substantially any angular poSition of said drive memberrelative to said brake member to provide immediate positive torquetransmission from said drive member to said shaft upon release of saidbraking means, means positioned on the other side of said drive memberfor urging said balls into said recesses, and means for simultaneouslyadjusting the force exerted by said means for urging said balls toprovide for conveniently and precisely adjusting the torque transmissionfrom said drive member to said shaft.
 2. A slip clutch as defined inclaim 1 wherein said drive member comprises a wheel having peripherallyspaced teeth and, said rotating means comprise a gear belt.
 3. A slipclutch as defined in claim 1 wherein said means forming said recesses,comprise a clutch plate positioned between said drive member and saidbrake member and having a generally uniform thickness, and means forsecuring said disc to said brake member.
 4. A slip clutch as defined inclaim 1 wherein said means for urging said balls into said recesses,comprise a plurality of compression springs extending within saidopenings within said drive member, an annular retaining membersurrounding said shaft and confining said springs within said openings,and means connecting said retaining member to said drive member forrotation therewith.
 5. A slip clutch as defined in claim 4 wherein saidadjustment means comprise a tubular threaded bushing secured to saidshaft for rotation therewith, and nut means adjustably mounted on saidbushing for confining said retaining member.
 6. An improved slip clutchcomprising a shaft, an annular drive member mounted on said shaft forrelative rotation, means for rotating said drive member, means defininga plurality of angularly spaced and generally axially extending openingswithin said drive member, a ball within each of said openings, anannular brake member secured to said shaft for rotation therewith, aclutch plate positioned axially between said drive member and said brakemember and secured to said brake member, said clutch plate having agenerally uniform thickness and a plurality of angularly spaced groovesin axially opposing relation to said balls within said drive member,means for braking the rotation of said brake member and said shaftcausing said balls to roll between said drive member and said brakemember, said grooves being arranged relative to said openings toposition at least one of said balls in seating relation within one ofsaid grooves at substantially any angular position of said drive memberrelative to said brake member to provide immediate positive torquetransmission from said drive member to said shaft upon release of saidbraking means, and means for adjusting the force exerted by said ballsagainst said clutch plate to provide for adjusting the torquetransmission from said drive member to said shaft.
 7. A slip clutch asdefined in claim 6 wherein each said groove is defined by convergingsurfaces defining an angle of approximately 120* therebetween.